October 1977 the first datasheet appeared and in January 1978 preproduction started. But the first models suffered from clumsy design of the power switch, which activated the light meter permanently. If the user forgot to switch the camera off, the battery was drained in just 15 hours. Furthermore, the PX-27 battery could be inserted the wrong way, causing damaged electronics. From August 1978 onward an improved model was made, where the light meter was only activated when the release button was depressed slightly. Advanced models Rollei 35 S Due to its large success, as early as the end of 1967 a luxury and a beginners variant of the Rollei 35 were planned. However, because of the production shift to Singapore, it was not until 1971 that the computation of a five-elements lens was assigned to Zeiss. This Sonnar f 2.8 / 40 mm lens was to be fitted with a front lens focusing control, like the Tessar, providing a similar mounting in the sliding tube. Only the two front lenses were to move when focusing. But, when finished, the lens did not focus sharply enough at close distances, and mass production had to be delayed by a whole year. The project was stopped and Zeiss designed a new lens with focusing control by moving the whole lens. Rollei's chief of development, Richard Weiß, concluded: "We've got into a precarious loss-making situation because of this. The developers have learned that, in the future, they must examine lenses, even if made by Carl Zeiss, with more scepticism." The tools for producing the new shutter mechanism were built by Prontor, a Zeiss subsidiary company in Calmbach, which had already taken over the manufacturing of the former shutter from Compur (another Zeiss subsidiary). Rollei 35 T When introducing the Rollei 35 S the former Rollei 35 was assigned the new name Rollei 35 T, without any further changes. A projected denim covered design variant, with an appropriate denim bag, was rejected because the textile covering frayed. Rollei 35 TE and Rollei 35 SE The original design did not have an exposure control in the viewfinder. The camera had to be taken away from the eye view, to observe the needle on the light meter. (This in fact wasn't a real disadvantage, because to focus the user also had to take the camera to the same position. In normal lighting conditions, the exposure settings of